Saturday 15 May 2021

Platyceps josephi: A new species of Racer from Tamil Nadu.

The Banded Racer, Argyrogena fasciolata, is a species of Colubrid Snake found across much of South Asia, which was first described in 1796 by the Scottish surgeon and naturalist Patrick Russell. Although widespread, the Banded Racer has a non-contiguous distribution (i.e. it's distribution is divided into many small local populations which do not connect) and is highly morphologically variable, which has led to repeated speculation that the 'species' may in fact represent a cluster of closely related species. This has led to many different classifications being proposed, but none of these have gained widespread acceptance, as taxonomists have been unable to agree on the criteria for describing new species, leaving to the retention of a single species to describe all populations, even though it is generally accepted that this is incorrect.

In a paper published in the journal Vertebrate Zoology on 13 May 2021, Veerappan Deepak of the Senckenberg Museum of Zoology, the Department of Life Sciences at the Natural History Museum, and the Centre for Ecological Sciences at the Indian Institute of Science, Surya Narayanan of the Suri Sehgal Centre for Biodiversity and Conservation of the Ashoka Trust for Research in Ecology and the Environment, Pratyush Mohapatra of the Central Zone Regional Centre of the Zoological Survey of India, Sushil Dutta of the Department of Zoology at Assam Don Bosco University, Gnanaselvan Melvinselvan of Dindugal in Tamil Nadu, Ashaharraza Khan of the Indian Herpetological Society, and Kristin Mahlow and Frank Tillack of the Museum für Naturkunde Berlin, describe a second species of Racer Snake from Tamil Nadu State, India.

Samples of tissue were extracted from samples Colubrid Snakes from across India and Pakistan, and DNA extracted from these using Qiagen DNeasy blood and tissue kits. They amplified partial sequences of two nuclear and three mitochondrial genes. Cytochrome b and NADH dehydrogenase subunit 4, 16S rRNA and the nu markers are oocyte maturation factor and recombination activating gene 1. 

Phylogenetic analyses were carried out using the CIPRES Science Gateway portal v3.3. PartitionFinder v2 was used (default MrBayes settings) to find the best-fit partition scheme for the concatenated dataset and model of sequence evolution for each partition. The best-fit scheme comprised six partitions. Deepak et al. estimated phylogenetic relationships using maximum likelihood and Bayesian inference.

Both the maximum likelihood and Bayesian inference found that the genus Platyceps was monophyletic (i.e. contained all the decendents of a single common ancestor) as long as the genus Argyrogena was included within it. For this reason they abolish the genus name Argyrogena, changing the formal name for the Banded Racer from Argyrogena fasciolata to Platyceps fasciolata. However, Deepak et al. note that the original name for the species was Natrix plinii, and that the species name should therefore now be Platyceps plinii.

The specimens sampled were found to fall into two distinct lineages, with one population comprising specimens from across Pakistan, northern, and central India, and one comprising specimens from Tamil Nadu State, in southern India. This population is therefore described as a new species, named Platyceps josephi (Joseph's Racer), in honour of the late Naveen Joseph, for his research on Reptiles, particularly Snakes in the Tuticorin region.

Map showing geomorphological features in parts of the Indian subcontinent and current locality records for Platyceps spp. mentioned in Deepak et al.'s study. Green (triangle) denotes the type locality and green (diamonds) for records of Platyceps plinii. Yellow (star) denotes the type locality, and yellow (circles) for the records of Platyceps josephi. Historically relevant names and important physiographic features are labelled. Deepak et al. (2021).

Platyceps josephi is a medium-sized Snake, with a maximum total length of 951 mm. It has a countersunk lower jaw, a dark brown dorsal service with white speckles, and two 'Π'-shaped white markings with black edges, on either side of the back of the head, behind the parietals, and extending into the body, and 34–48 prominent white bands on the body in both juveniles and adults. The body of Platyceps josephi is subcylindrical, being somewhat dorsoventrally flattened. The head is ovate, and barely wider than the anterior end of body. 

Platyceps josephi in life from various parts of Tamil Nadu state, India: (A) Holotype NCBS-AU732 (female, snout-vent length: 757 mm) from Tuticorin, (B) Paratype NCBS-AU733 (female, snout-vent length: 608 mm) from Tuticorin, (C) Paratype BNHS 3516 (female, snout-vent length: 592 mm) from Tuticorin, (D) uncollected (juvenile) from Tuticorin, (E) Paratype ZSI-CZRC-6639 (male, snout-vent length: 574 mm) from Karur, (F) Uncollected (male) from Vathalagundu, (G) uncollected (juvenile) from Tuticorin and (H) uncollected (female, snout-vent length: 655 mm) from Pollachi. Deepak et al. (2021).

Platyceps josephi is so far only known from Tamil Nadu State, India. It is reported from the Anaimallai Hills and different localities within the districts of Coimbatore (Anaikatti, Coimbatore, Pollachi), Dindigul (Batlagundu), Kanyakumari (Maruthuvazhmalai), Karur (Karur), Madurai (Madurai, Vadipatti), Salem (Salem), Theni (Meghamalai Hills), Thoothukudi (Tuticorin), Tirunelveli (Coutrallam, Manimutharu, Tirunelveli) and Villupuram (Auroville). The new species mostly inhabits open habitats with sandy or rocky patches in grasslands and scrublands in both inland and coastal areas of Tamil Nadu from elevations between 10 and 580 m above sealevel. Most of the areas where the species occurs receive less than 500 mm annual rainfall except locations near the rain shadowed areas close to the Western Ghats receives higher rainfall. The species is generally observed under thorny bushes, rock boulders, paddy fields, heaps of dry Coconut fronds and seen crossing roads, although several specimens were collected from Human habitations.

Habitats of Platyceps josephi in Tamil Nadu state, India: (A) close to the coast at the type locality Tuticorin, and (B) inland habitat near Anaikatti, Coimbatore. Deepak et al. (2021).

Platyceps josephi is a diurnal Snake, terrestrial and swift in locomotion. There is a report of arboreal behaviour under artificial conditions, but this is not known in the wild. It is an aggressive Snake, flattening its head as a mock hood display mimicking a Cobra, when agitated and biting freely, but it becomes docile after a few days in captivity.

The diet of the Platyceps josephi chiefly consists of Geckos, Lizards and small Rodents. It has been observed to kill the prey by constricting and/or crushing the prey against ground or tree trunk. In all captive observations, it swallows the prey from the head first. It is an oviparous Snake with few records of clutch sizes, 7–12 eggs during the month of March and June and have been reported, with the eggs being 40 mm in length. Females are reported to lay their eggs in bunds (raised areas surrounding the paddy fields) of paddy fields. 

Platyceps josephi is reported only from one protected area (the Megamalai Wildlife Sanctuary) in its known range. The species faces a number of threats across its distributional range, including habitat destruction, because the grasslands in southern Tamil Nadu are being actively converted into plantations, farmlands and urbanisation. Although there are records from such converted plantations and Human settlements, the species’ ability to adapt and its reproductive success is not known. Rocky habitats in Madurai region are also highly affected by the mining activities and road traffic is another important threat to Platyceps josephi. Three out of the seven specimens collected by Deepak et al. were roadkill and six other uncollected roadkill specimens were observed from various parts of Tamil Nadu between 2017 and 2020. The Area Of Occupancy of Platyceps josephi is 72 000 km² and Extent Of Occupancy is 70 698 km². Even though this is a relatively large area of distribution for a species, Deepak et al.'s field surveys and records suggest that this species has patchy distribution within its range. Also, much of the habitat in these regions where Platyceps josephi is reported are under severe threats like conversion of grasslands to farmlands, widescale monoculture plantations (Eucalyptus sp.) and urbanization. Given this information, Deepak et al. suggest that Platyceps josephi should be considered to be Vulnerable under the terms of the International Union for the Conservation of Nature’s Red List of Threatened Species.

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